Doesn’t look like the pole was gal at all, just painted mild steel. That stirrup will work but will rust again but that’s okay as you can replace it easily enough if you are still around.

when you afix the stirrup (get a better one with a foot and chip concrete flat with a cold chisel, use SS bolts, brush and rust proof paint the bit where you cut the support off, just prop the joist with a log (or whatever) and a jack as you are working. It will look ghetto but be solid. You don’t want the fasteners taking the load, that’s what the foot of the stirrup is for.

I am not a builder, just what i’d do ;)